Populations

A population is a group of organisms of the same species living in the same place at the same time. Populations evolve according to their own self interest in a particular environment.

Factors which can limit the growth of a population include: Predation Shortage of food Disease Lack of water Lack of space Disaster

Carrying Capacity Look at the picture. How do you think this is an analogy for carrying capacity?

Carrying Capacity The largest number of individuals in a species that an environment can support

Activities Question sheet (page 4) Question sheet (page 4) Activity Activity

Competition Ecosystems have limited resources. Organisms with similar needs must compete to get the resources they need. Competition occurs between: Members of the same species = Intraspecific competition Members of different species = Interspecific Competition Activity Time!

Follow Up After we combined tweezers and tongs, did you get more or less beans? Why? After we combined tweezers and tongs, did you get more or less beans? Why? What are the challenges of intraspecific vs interspecific competition? What are the challenges of intraspecific vs interspecific competition?

Limiting Factors An organisms’ need for space depends on their size, environment, and way of life. This need for space determines the carrying capacity of a specific organism. Factors affecting population size may be: Density-Dependent Factors Density-Independent Factors

Density Dependent Factors If population density increases, it can cause a decrease in the population. Population density measures the # of individuals of a particular species per unit of area or volume Some examples of density dependent limiting factors: Competition Competition Predation Predation Disease Disease Intrinsic factors (mice) Intrinsic factors (mice)

Density Independent Factors Events that can decrease population size that are not related to how many individuals are in the population to begin with: Pollution Forest fire Flood Volcano Extreme weather

Activity Hand out limiting factors assignment Hand out limiting factors assignment

Characteristics of Populations Population Size and Density

Size vs Density Population size measures the # of individuals of a particular species in a given region Population density measures the # of individuals of a particular species per unit of area or volume Population dispersion measures the general pattern in which individuals are distributed throughout a given region

Population Density Density (D) = # of individuals (N)/unit total area (S)

Example During the Walking Dead, Atlanta, a city km 2, was populated with 4000 zombies. What is the population density of zombies in Atlanta? During the Walking Dead, Atlanta, a city km 2, was populated with 4000 zombies. What is the population density of zombies in Atlanta?

Activity Sheet

Population Dispersion Additionally, the population can disperse in different ways Additionally, the population can disperse in different ways Random Random Clumped Clumped Uniform Uniform Let’s model each type with volunteers

Population Dispersal Patterns of distribution are usually species-specific but may derive from a variety of causes: Patterns of distribution are usually species-specific but may derive from a variety of causes: Uniform dispersal pattern is likely to result from direct competition or territoriality. Penguins often exhibit uniform spacing by aggressively defending their territory among their neighbors Uniform dispersal pattern is likely to result from direct competition or territoriality. Penguins often exhibit uniform spacing by aggressively defending their territory among their neighbors Random distribution the lack of any strong social interactions between species (dandelions seeds dispersed by the wind) Random distribution the lack of any strong social interactions between species (dandelions seeds dispersed by the wind) Clumped pattern could result from behavior (pack animals), or a very spotty arrangement of suitable habitat (animals need certain resources to survive. When resources are rare animals tend to “clump” together around these resources Clumped pattern could result from behavior (pack animals), or a very spotty arrangement of suitable habitat (animals need certain resources to survive. When resources are rare animals tend to “clump” together around these resources

Population Growth (r) If unlimited resources are present, growth will be exponential If unlimited resources are present, growth will be exponential It will proceed very quickly for rapidly reproducing organisms and more slowly for slowly reproducing ones It will proceed very quickly for rapidly reproducing organisms and more slowly for slowly reproducing ones The curve, however, will always be a “J” curve or an exponential growth curve The curve, however, will always be a “J” curve or an exponential growth curve

Population Growth 2 Resources are never unlimited, though. Resources are never unlimited, though. As population rises, resources decline. As population rises, resources decline. If the growth is too rapid, resources are rapidly depleted and a population crash can occur If the growth is too rapid, resources are rapidly depleted and a population crash can occur This pattern occurs often with many populations (including humans) This pattern occurs often with many populations (including humans) For example... For example... Gypsy moth caterpillar

Population Growth 3 More often what happens is that the resources slowly decrease, the growth rate slowly decreases, and they meet. More often what happens is that the resources slowly decrease, the growth rate slowly decreases, and they meet. This point that they oscillate around is the carrying capacity of the environment for that particular organism This point that they oscillate around is the carrying capacity of the environment for that particular organism So when would you “harvest” these individuals? (1,2,3,4,or 5) So when would you “harvest” these individuals? (1,2,3,4,or 5) S - shaped curve

Activity Work sheet Work sheet Rabbit activity Rabbit activity

Factors That Affect Population Growth Populations experience natural hourly, daily, seasonal, and annual fluctuations in numbers. Populations experience natural hourly, daily, seasonal, and annual fluctuations in numbers. Population size changes due to: Population size changes due to: Births Births Deaths= POPULATION Deaths= POPULATION Immigration DYNAMICS Immigration DYNAMICS Emigration Emigration

Which country looks like it is experiencing exponential growth? Which country looks like it has reached its carrying capacity? Because it has reached its carrying capacity, describe the relationship between its birth rates and death rates Describe what is happening to Europe’s population size in terms of birth rates and death rates. Which country or countries could be experiencing: emigration: immigration:

r - Selected Species Bacteria Bacteria Pest insects Pest insects Diatoms Diatoms Small Rodents Small Rodents

K - Selected Species Most birds Most birds Most predators Most predators Elephants Elephants Whales Whales Oaks Oaks Chestnuts Chestnuts Apple Apple Coconut Coconut

In groups Based on the examples of r selected and k selected species from the previous slides, brainstorm characteristics you think are shared amongst each type of species. Based on the examples of r selected and k selected species from the previous slides, brainstorm characteristics you think are shared amongst each type of species.

r – selected Species In unstable or unpredictable environments r-selection predominates In unstable or unpredictable environments r-selection predominates Traits that are thought to be characteristic of r-selection include: Traits that are thought to be characteristic of r-selection include: high fecundity (potential for reproduction in one lifetime), high fecundity (potential for reproduction in one lifetime),fecundity small body size, small body size,body sizebody size short generation time, short generation time, ability to disperse offspring widely. ability to disperse offspring widely.disperse

k-selected Species In stable or predictable environments k-selection predominates In stable or predictable environments k-selection predominates Typically are very constant and close to the maximum that the environment can bear. Typically are very constant and close to the maximum that the environment can bear. Traits that are thought to be characteristic of k-selection include: Traits that are thought to be characteristic of k-selection include: large body size, large body size, long life expectancy, long life expectancy,life expectancylife expectancy production of fewer offspring that require extensive parental care until they mature. production of fewer offspring that require extensive parental care until they mature.

Video hill.com/sites/ /student_view0/chap ter55/animation_-_r_and_k_strategies.html hill.com/sites/ /student_view0/chap ter55/animation_-_r_and_k_strategies.html hill.com/sites/ /student_view0/chap ter55/animation_-_r_and_k_strategies.html hill.com/sites/ /student_view0/chap ter55/animation_-_r_and_k_strategies.html

Group Discussion Why are pest species likely to be extreme r-selected species? Why are many endangered species likely to be extreme K-selected species. Why are pest species likely to be extreme r-selected species? Why are many endangered species likely to be extreme K-selected species.

Journal Entry Given current environmental conditions, if you had a choice would you rather be an r-strategist or a K- strategist? Explain your answer. What implications does your decision have for your current lifestyle? Given current environmental conditions, if you had a choice would you rather be an r-strategist or a K- strategist? Explain your answer. What implications does your decision have for your current lifestyle?